For example, a MEMS device having a supporting member formed of a silicon substrate, a fixing portion formed on the supporting member, and a flat plate-shaped movable portion provided with interposing a space between the movable portion and the supporting member, in which the fixing portion supports the movable portion via a beam, has been suggested. This MEMS device detects a displacement of the movable portion as a change of a capacitance value.
In the method of forming the MEMS device, the space of the MEMS device is formed by removing a sacrificial layer provided between the supporting member and the movable portion and beam, and a cavity in a cavity layer formed by the removal corresponds to the space. However, in the course of the manufacturing process or during use of the product, a sticking phenomenon in which the beam comes into contact with the supporting member occurs in some cases. Thus, in the semiconductor sensor and the manufacturing method thereof already known to the public based on the specification of Japanese Patent Application Laid-Open Publication No. 2001-4658 (Patent Document 1), a silicon wafer (silicon substrate) having a concave portion formed thereon is first attached onto a glass substrate serving as a supporting member, thereby forming a cavity layer. Then, the silicon wafer is subjected to anisotropic etching to form functional portions such as a fixing portion, a beam, and a movable portion. Therefore, since the etching of a sacrificial layer is not required, the occurrence of the sticking phenomenon can be reduced.
Also, in the method of manufacturing a MEMS device already known to the public based on the specification of Japanese Patent Application Laid-Open Publication No. 10-178181 (Patent Document 2), a concave portion is first formed on a glass substrate. Then, a silicon wafer (silicon substrate) having an oxide film on one surface thereof and a nickel film to be used as a mask in silicon etching on the other surface thereof is fabricated. Thereafter, the nickel mask is patterned and the silicon wafer is subjected to anisotropic etching with using the nickel film as a mask, thereby forming a movable portion. At this time, the oxide film formed on the opposite surface is used as an etch stop layer. After the anisotropic etching to the silicon wafer, the nickel layer used as the mask is removed from the silicon wafer, and then the silicon wafer is anodically-bonded to the glass substrate. Thereafter, the oxide film on the surface of the silicon wafer is removed.
Note that, in the MEMS device, as introduced in the Patent Documents 1 and 2, an SON (Silicon On Nothing) wafer (SON substrate) is used. As an example of the manufacturing method thereof, the SON wafer can be formed by bonding a flat wafer (glass substrate) onto one silicon wafer (silicon substrate) having a concave portion formed thereon. Further, other than these methods, the SON wafer can be fabricated by the manufacturing methods introduced in Applied Physics Letters, Vol. 77, No. 20, 2000, pp. 3290-3292 (Non-Patent Document 1) and Journal of Vacuum Science and Technology A 18(4), 2000, pp. 1853-1858 (Non-Patent Document 2). The Non-Patent Document 1 introduces a process of forming a space (cavity) by deeply digging a micro-hole on the order of sub-microns in the surface of a silicon wafer and then performing hydrogen-annealing. Also, although the Non-Patent Document 2 does not describe a method of manufacturing a SON wafer, it describes a process that can be applied to the SON manufacture as it is.